1. Field of the Invention
This invention is related to a carry table generating method, and more particularly to a method of generating a carry table suitable for being applied to a dithering process.
2. Description of Related Art
A frequently encountered problem in displaying a digital image is that the gray level resolution of a display device is smaller than that of an original image. Therefore, the data width used by the internal operation of the display device is usually greater than the data width used by the input/output ports thereof. Under such conditions, the display device has to use dithering process in order to decrease the data width of its outputted pixel gray value.
Dithering is to utilize the property that human eyes automatically do average calculations on gray values of small regions when viewing from a long distance, so as to make a display screen show more color gradations. In addition, a common dithering process is to remove the lower bits in a pixel gray value, for example, the least significant bit (LSB), and then to determine if the pixel gray value should plus one according to a dither carry table.
For example, the lower 4 bits in a pixel gray value may be rounded off in a dithering process. In addition, to compensate for the rounded-off 4 bits, the dithering process has to make the display screen display 1/16 gray level. Therefore, such a dithering process has to record each single color by using 16 dither carry tables with a size of 16×16. In addition, a conventional carry table generating method is to directly read 16 dither carry tables with a size of 16×16 from a memory. In other words, a memory of 16×16×16 bits, i.e. 512 bytes, is required for storing 16 dither carry tables. As a result, however, huge memory space will be consumed for generating the required dither carry tables.